1. Field of the Invention
The present invention relates to a method of operating an ink jet recording head. More particularly, the present invention relates to a method of operating an ink jet recording head arranged in such a manner that energy generating bodies for discharging ink are connected to one another in series.
2. Related Background Art
Hitherto, a so-called thermal ink jet recording head (referred to as an "ink jet recording head" hereinafter) for discharging ink by heating reveals an advantage in that a multiplicity of nozzles can integrally be constituted since the structure of each nozzle can be simplified and the size of the same can be reduced. Therefore, a plurality of nozzles have been integrally formed so as to be used in a printer for obtaining a high density record at high speed.
An ink jet recording head of the type described above must quickly operate its electrothermal converting body (also called a "heat emitting element" hereinafter), which serves as an energy generating means for generating ink discharging energy, in a short time for the purpose of effectively discharging ink. In general, the heat emitting element is operated by a short electric current pulse of several microseconds. Therefore, a large electric current flows at the time the heat emitting element commences operation. As a result, if a plurality of heat emitting elements are connected to one another with fine common wiring patterns, a voltage drop will take place in the common wirings. Therefore, a problem arises in that the operating conditions can undesirably vary in accordance with the number of the heat emitting elements which are operated simultaneously.
Accordingly, the following structures capable of overcoming the above-described problem have been known.
(1) Two wiring patterns through which positive and negative electric currents flow are provided for each of the heat emitting elements provided in the ink jet recording head. Furthermore, a protection layer made of a protecting material is provided so that the wiring patterns and the heat emitting elements are protected from the damage due to the electrochemical reaction. PA0 (2) As disclosed in Japanese Patent Laid-Open No. 64-38245 when the heat emitting elements are operated, the signal for operating the heat emitting elements is divided into a plurality of pulse signals having a positive or negative potential with respect to a reference potential applied to the common electrode of the heat emitting elements. The thus divided pulse signals are applied to the selected electrode of the heat emitting element to be operated. PA0 (3) As disclosed in U.S. Pat. No. 4,463,359, a plurality of heat emitting elements, which are disposed in a zigzag manner, are operated via a diode matrix. A method of operating the thus disposed heat emitting elements has been disclosed in Japanese Patent Laid-Open 49-105544 and 51-94940 in which the plurality of the heat emitting elements are divided into two blocks, predetermined heat emitting elements being alternately or simultaneously operated for each block. PA0 (4) A structure has been disclosed in Japanese Patent Laid-Open No. 62-290557 by the applicant of the present invention in which, in a thermosensitive recording head, wirings of the number which is larger, by one, than the number of the plurality of heat emitting elements provided for the thermal head are used to establish the connections between the heat emitting elements and the operating portion to operate the heat emitting elements. PA0 (1) In the case where the two wiring patterns are provided for each of the heat emitting elements, wiring patterns numbering twice the number of the heat emitting elements must be provided. Therefore, the discharge ports cannot be easily mounted at a high density on the substrate of the ink jet recording head. Therefore, a critical problem arises when a precise image is desired. PA0 (2) The structure disclosed in Japanese Patent Laid-Open No. 64-38245 is capable of preventing the breakage of the ink jet recording head due to the above-described electrochemical reaction since a positive or negative pulse is applied to the selected electrode. However, the problem of the voltage dropping due to the enlargement of the electric resistance at the wiring pattern and the resulted problem of the heating value in the ink jet recording head cannot be overcome. Furthermore, since the positive and negative pulses are generated as the operating signals, a plurality of operating power sources must be provided, thereby causing the size of the apparatus to be enlarged excessively and the structure to become too complicated. PA0 (3) In the case of the structure disclosed in U.S. Pat. No. 4,463,359, in which the heat emitting elements disposed in a zigzag manner are operated via the diode matrix, the existence of the diode matrix will restrict the direction in which the operating voltage is applied to the heat emitting element or the direction in which the operating current flows. Therefore, the problem arises in that the wiring patterns and the heat emitting elements become corroded. What is worse, the specific crosstalk of the diode matrix will cause heat emitting elements other than the specified heat emitting elements to generate heat. As a result, the heating value in the ink jet recording head can be increased and the operation of the heating elements may become unstable. PA0 (4) In a case where the operating method for use in the thermal head disclosed in Japanese Patent Laid-Open No. 62-290557 is employed in an ink jet recording head which records data by utilizing heat, a relatively large current flows in the heat emitting element of the ink jet recording head. Therefore, a problem arises in that the electric current flowing in the wiring pattern which connects the heat emitting element to the operating portion cannot be made constant. As a result, the voltage drop, which takes place in the wiring pattern will sometimes change. Therefore, the operating conditions for the heat emitting element cannot be stabilized. Furthermore, when the heat emitting element of an ink jet recording head which utilizes heat is operated at a repeated frequency of several KHz, it is preferable to supply electricity to the heat emitting element for several microseconds up to 10 .mu.sec. The electric current, which instantaneously flows during that time so as to obtain the energy to discharge ink, is enlarged. PA0 (5) In the conventional ink jet recording apparatus, the ink jet recording head is operated in response to the image signal in such a manner that the image signal supplied as serial data is converted into parallel data by using a shift register so that the heat elements of the nozzles (ink passages) are operated to discharge ink. Therefore, the time width of the image signal cannot be changed individually from the selecting operation of the heat emitting elements. As a result, the heating value of the heat emitting elements cannot be controlled individually.
Furthermore, the direction in which the operating current flows in the heat emitting element is not constant during operation.
However, the above-described conventional structures encounter the following problems.
If the heat emitting elements are formed at a high density, the thickness of each of the wiring patterns must be reduced because the number of the heat emitting elements is increased. This leads to the fact that electric resistance at the wiring pattern is excessively enlarged, causing the heating value to be enlarged excessively. As a result, the temperature at the inside portion of the ink jet recording head is raised excessively.
The thickness of the protection layer for protecting the wiring pattern and the heat emitting elements must be formed sufficiently large. However, the existence of even an extremely small pinhole will cause corrosion of a thin wiring pattern or the heat emitting elements to take place. The corrosion occurs because a positive or negative potential is repeatedly applied to that point in accordance with the potential applied to the two wiring patterns. As a result, the ink jet recording head will be broken. If the thickness of the protection layer is enlarged in order to strengthen the protection layer, heat generated in the heat emitting element cannot be easily transmitted to the ink. In consequence, a critical problem arises when a large ink-discharging force is desired. Therefore, ink cannot be discharged when the ink used has a high viscosity or the components of the ink have been changed due to evaporation or the like.
Furthermore, according to this operating method, the plurality of the heat emitting elements are divided into two blocks. In this case, the ink discharging timing is different for each of the blocks. As a result, when the ink jet recording head is relatively moved with respect to the recording medium so as to perform recording, the position at which ink adheres is deviated in the direction in which the ink jet recording head moves. As a result, the quality of the recorded image deteriorates.
Therefore, when the method of operating the thermal head is employed, the selection operations for all of the heat emitting elements must be performed simultaneously and the selected heat emitting elements must be operated simultaneously. Therefore, the instantaneous current becomes too large, causing the heating value of the ink jet recording head to be enlarged excessively. Furthermore, the discharging operation becomes unstable.